The navel orange is a variety of orange with a characteristic second fruit at the apex, which protrudes slightly like a human navel. This variety first was caused by a mutation in an orange tree, and first appeared in the early 19th century at a monastery in Bahia, Brazil.[1] The mutation caused the orange to develop a second fruit at its base, opposite the stem, embedded within the peel of the primary orange.[2] This mutation also caused it to be seedless,[1][3] meaning the only way the plant can be propogated is by cutting and grafting.[2][4]
Navel oranges are mainly an eating fruit because they are seedless and their thicker skin makes them easy to peel.[5] They are also less suitable for juice than other orange varieties as they are less juicy, and because their flesh contains limonin, which becomes bitter when exposed to air.[6][7]